Barrier movement operators are automated systems which are used to move a barrier with respect to an opening. Examples of barriers to be moved include garage doors, gates, fire doors and rolling shutters. A number of barrier movement operators have been sold over the years most of which include a head unit containing a motor connected to a transmission. The transmission, which may include, for example, a belt drive, a chain drive, a screw drive or extendible arm is then coupled to the barrier for opening and closing.
Such barrier movement operators also typically include a wall control unit, which is connected to send signals to the head unit thereby causing the head unit to open and close the barrier. In addition, these operators often include a receiver unit at the head unit to receive wireless transmissions from a hand-held code transmitter or from a keypad transmitter, which may be affixed to the outside of the area closed by the barrier or other structure.
Obstructions may exist or may enter the pathway of the moveable barrier. Previous systems have allowed the barrier operator systems to determine if an obstruction has been encountered and to either stop or reverse the direction of the travel of the barrier once this determination has been made. For instance, some previous systems measured the force applied to the barrier by the motor. The systems then compared the measured force to an expected value plus a fixed cushion value. If the comparison indicated that the measurement value exceeded the expected value plus the cushion value (together, a threshold value), then the downward barrier movement was reversed. These systems typically determined the force by measuring the barrier speed or current in the motor and then calculated the force using these measurements.
In some previous systems, capacitive sensor arrangements were used to detect the obstruction in the pathway of the door by detecting the capacitance between a conductive element and the ground. However, in these previous systems, the sensed capacitance between a conductive element and the ground increases above a threshold as the sensor approaches the ground thereby indicating that an “obstruction” existed. Consequently, as the door neared the ground, the capacitance reading would have to be adjusted or discarded because the reading would indicate an obstruction existed, when, in fact, the ground was the “obstruction” being detected. Thus, these previous systems could not be used to detect an obstruction unless the readings were sufficiently adjusted to take into account the detection of the ground or other reference.